What is the standard Apple blue colour?

Try the digital color meter? It seems to think (14, 122, 254).

Then add a category:

@implementation UIColor (MyColors)

+ (UIColor*)appleBlue {
    return [UIColor colorWithRed:14.0/255 green:122.0/255 blue:254.0/255 alpha:1.0];
}

@end

Since iOS 7 you can simply use this:

UIColor.systemBlue

A bit late, but you can find the colour values in Apple's Human interface guidelines.

The blue is (R, G, B) = (0, 122, 255) = #007AFF

I created a GIST with UIColor extension for your convenience.